test w/ custom labels

Author: asherf

README.md

@@ -204,6 +204,16 @@ that will export the metrics (replace myapp by your project name).
 
 Then we inject the wrapper in settings:
 
-```python 
+```python
 ROOT_URLCONF = "graphite.urls_prometheus_wrapper"
 ```
+
+## Adding custom labels to middleware (request/response) metrics
+
+You can add application specific labels to metrics reported by the django-prometheus middleware.
+This involves extending the classes defined in middleware.py.
+
+* Extend the Metrics class and override the `register_metric` method to add the application specific labels.
+* Extend middleware classes, set the metrics_cls class attribute to the the extended metric class and override the label_metric method to attach custom metrics.
+
+See implementation example in [the test app](django_prometheus/tests/end2end/testapp/test_middleware_custom_labels.py#L19-L46)

django_prometheus/middleware.py

@@ -25,7 +25,7 @@
 )
 
 
-class Metrics:
+class Metrics(object):
     _instance = None
 
     @classmethod

django_prometheus/tests/end2end/testapp/test_middleware_custom_labels.py

@@ -1,3 +1,6 @@
+from prometheus_client import REGISTRY
+from prometheus_client.metrics import MetricWrapperBase
+
 from django.test import SimpleTestCase, override_settings
 from django_prometheus.middleware import (
     Metrics,
@@ -9,8 +12,8 @@
 from testapp.test_middleware import M, T
 
 EXTENDED_METRICS = [
-    "django_http_requests_latency_seconds_by_view_method",
-    "django_http_responses_total_by_status_view_method",
+    M("requests_latency_seconds_by_view_method"),
+    M("responses_total_by_status_view_method"),
 ]
 
 
@@ -19,7 +22,7 @@ def register_metric(
         self, metric_cls, name, documentation, labelnames=tuple(), **kwargs
     ):
         if name in EXTENDED_METRICS:
-            labelnames = labelnames + ("view_type", "user_agent_type")
+            labelnames.extend(("view_type", "user_agent_type"))
         return super(CustomMetrics, self).register_metric(
             metric_cls, name, documentation, labelnames=labelnames, **kwargs
         )
@@ -33,26 +36,30 @@ class AppMetricsAfterMiddleware(PrometheusAfterMiddleware):
     metrics_cls = CustomMetrics
 
     def label_metric(self, metric, request, response=None, **labels):
+        new_labels = labels
         if metric._name in EXTENDED_METRICS:
-            labels.update({"view_type": "foo", "user_agent_type": "browser"})
+            new_labels = {"view_type": "foo", "user_agent_type": "browser"}
+            new_labels.update(labels)
         return super(AppMetricsAfterMiddleware, self).label_metric(
-            metric, request, response=response, **labels
+            metric, request, response=response, **new_labels
         )
 
 
 @override_settings(
-    MIDDLEWARE_X=get_middleware(
+    MIDDLEWARE=get_middleware(
         "testapp.test_middleware_custom_labels.AppMetricsBeforeMiddleware",
         "testapp.test_middleware_custom_labels.AppMetricsAfterMiddleware",
     )
 )
 class TestMiddlewareMetricsWithCustomLabels(PrometheusTestCaseMixin, SimpleTestCase):
-    """Test django_prometheus.middleware.
-
-    Note that counters related to exceptions can't be tested as
-    Django's test Client only simulates requests and the exception
-    handling flow is very different in that simulation.
-    """
+    @classmethod
+    def setUpClass(cls):
+        super(TestMiddlewareMetricsWithCustomLabels, cls).setUpClass()
+        # Allow CustomMetrics to be used
+        for metric in Metrics._instance.__dict__.values():
+            if isinstance(metric, MetricWrapperBase):
+                REGISTRY.unregister(metric)
+        Metrics._instance = None
 
     def test_request_counters(self):
         registry = self.saveRegistry()
@@ -99,6 +106,8 @@ def test_request_counters(self):
             status="200",
             view="testapp.views.index",
             method="GET",
+            view_type="foo",
+            user_agent_type="browser",
         )
         self.assertMetricDiff(
             registry,
@@ -107,4 +116,6 @@ def test_request_counters(self):
             status="200",
             view="testapp.views.help",
             method="GET",
+            view_type="foo",
+            user_agent_type="browser",
         )